import struct
import time

from pymodbus.exceptions import ModbusIOException
from pymodbus.exceptions import InvalidMessageReceivedException
from pymodbus.utilities import checkCRC, computeCRC
from pymodbus.utilities import hexlify_packets, ModbusTransactionState
from pymodbus.compat import byte2int
from pymodbus.framer import ModbusFramer, FRAME_HEADER, BYTE_ORDER

# --------------------------------------------------------------------------- #
# Logging
# --------------------------------------------------------------------------- #
import logging
_logger = logging.getLogger(__name__)

RTU_FRAME_HEADER = BYTE_ORDER + FRAME_HEADER


# --------------------------------------------------------------------------- #
# Modbus RTU Message
# --------------------------------------------------------------------------- #
class ModbusRtuFramer(ModbusFramer):
    """
    Modbus RTU Frame controller::

        [ Start Wait ] [Address ][ Function Code] [ Data ][ CRC ][  End Wait  ]
          3.5 chars     1b         1b               Nb      2b      3.5 chars

    Wait refers to the amount of time required to transmit at least x many
    characters.  In this case it is 3.5 characters.  Also, if we receive a
    wait of 1.5 characters at any point, we must trigger an error message.
    Also, it appears as though this message is little endian. The logic is
    simplified as the following::

        block-on-read:
            read until 3.5 delay
            check for errors
            decode

    The following table is a listing of the baud wait times for the specified
    baud rates::

        ------------------------------------------------------------------
         Baud  1.5c (18 bits)   3.5c (38 bits)
        ------------------------------------------------------------------
         1200   13333.3 us       31666.7 us
         4800    3333.3 us        7916.7 us
         9600    1666.7 us        3958.3 us
        19200     833.3 us        1979.2 us
        38400     416.7 us         989.6 us
        ------------------------------------------------------------------
        1 Byte = start + 8 bits + parity + stop = 11 bits
        (1/Baud)(bits) = delay seconds
    """

    def __init__(self, decoder, client=None):
        """ Initializes a new instance of the framer

        :param decoder: The decoder factory implementation to use
        """
        self._buffer = b''
        self._header = {'uid': 0x00, 'len': 0, 'crc': '0000'}
        self._hsize = 0x01
        self._end = b'\x0d\x0a'
        self._min_frame_size = 4
        self.decoder = decoder
        self.client = client

    # ----------------------------------------------------------------------- #
    # Private Helper Functions
    # ----------------------------------------------------------------------- #
    def decode_data(self, data):
        if len(data) > self._hsize:
            uid = byte2int(data[0])
            fcode = byte2int(data[1])
            return dict(unit=uid, fcode=fcode)
        return dict()

    def checkFrame(self):
        """
        Check if the next frame is available.
        Return True if we were successful.

        1. Populate header
        2. Discard frame if UID does not match
        """
        try:
            self.populateHeader()
            frame_size = self._header['len']
            data = self._buffer[:frame_size - 2]
            crc = self._buffer[frame_size - 2:frame_size]
            crc_val = (byte2int(crc[0]) << 8) + byte2int(crc[1])
            if checkCRC(data, crc_val):
                return True
            else:
                _logger.debug("CRC invalid, discarding header!!")
                self.resetFrame()
                return False
        except (IndexError, KeyError, struct.error):
            return False

    def advanceFrame(self):
        """
        Skip over the current framed message
        This allows us to skip over the current message after we have processed
        it or determined that it contains an error. It also has to reset the
        current frame header handle
        """
        try:
            self._buffer = self._buffer[self._header['len']:]
        except KeyError:
            #   Error response, no header len found
            self.resetFrame()
        _logger.debug("Frame advanced, resetting header!!")
        self._header = {}

    def resetFrame(self):
        """
        Reset the entire message frame.
        This allows us to skip over errors that may be in the stream.
        It is hard to know if we are simply out of sync or if there is
        an error in the stream as we have no way to check the start or
        end of the message (python just doesn't have the resolution to
        check for millisecond delays).
        """
        _logger.debug("Resetting frame - Current Frame in "
                      "buffer - {}".format(hexlify_packets(self._buffer)))
        self._buffer = b''
        self._header = {}

    def isFrameReady(self):
        """
        Check if we should continue decode logic
        This is meant to be used in a while loop in the decoding phase to let
        the decoder know that there is still data in the buffer.

        :returns: True if ready, False otherwise
        """
        return len(self._buffer) > self._hsize

    def populateHeader(self, data=None):
        """
        Try to set the headers `uid`, `len` and `crc`.

        This method examines `self._buffer` and writes meta
        information into `self._header`. It calculates only the
        values for headers that are not already in the dictionary.

        Beware that this method will raise an IndexError if
        `self._buffer` is not yet long enough.
        """
        data = data if data else self._buffer
        self._header['uid'] = byte2int(data[0])
        func_code = byte2int(data[1])
        pdu_class = self.decoder.lookupPduClass(func_code)
        size = pdu_class.calculateRtuFrameSize(data)
        self._header['len'] = size
        self._header['crc'] = data[size - 2:size]

    def addToFrame(self, message):
        """
        This should be used before the decoding while loop to add the received
        data to the buffer handle.

        :param message: The most recent packet
        """
        self._buffer += message

    def getFrame(self):
        """
        Get the next frame from the buffer

        :returns: The frame data or ''
        """
        start = self._hsize
        end = self._header['len'] - 2
        buffer = self._buffer[start:end]
        if end > 0:
            _logger.debug("Getting Frame - {}".format(hexlify_packets(buffer)))
            return buffer
        return b''

    def populateResult(self, result):
        """
        Populates the modbus result header

        The serial packets do not have any header information
        that is copied.

        :param result: The response packet
        """
        result.unit_id = self._header['uid']
        result.transaction_id = self._header['uid']

    # ----------------------------------------------------------------------- #
    # Public Member Functions
    # ----------------------------------------------------------------------- #
    def processIncomingPacket(self, data, callback, unit, **kwargs):
        """
        The new packet processing pattern

        This takes in a new request packet, adds it to the current
        packet stream, and performs framing on it. That is, checks
        for complete messages, and once found, will process all that
        exist.  This handles the case when we read N + 1 or 1 // N
        messages at a time instead of 1.

        The processed and decoded messages are pushed to the callback
        function to process and send.

        :param data: The new packet data
        :param callback: The function to send results to
        :param unit: Process if unit id matches, ignore otherwise (could be a
               list of unit ids (server) or single unit id(client/server)
        :param single: True or False (If True, ignore unit address validation)

        """
        if not isinstance(unit, (list, tuple)):
            unit = [unit]
        self.addToFrame(data)
        single = kwargs.get("single", False)
        if self.isFrameReady():
            if self.checkFrame():
                if self._validate_unit_id(unit, single):
                    self._process(callback)
                else:
                    _logger.debug("Not a valid unit id - {}, "
                                  "ignoring!!".format(self._header['uid']))
                    self.resetFrame()
            else:
                _logger.debug("Frame check failed, ignoring!!")
                self.resetFrame()
        else:
            _logger.debug("Frame - [{}] not ready".format(data))

    def buildPacket(self, message):
        """
        Creates a ready to send modbus packet

        :param message: The populated request/response to send
        """
        data = message.encode()
        packet = struct.pack(RTU_FRAME_HEADER,
                             message.unit_id,
                             message.function_code) + data
        packet += struct.pack(">H", computeCRC(packet))
        message.transaction_id = message.unit_id  # Ensure that transaction is actually the unit id for serial comms
        return packet

    def sendPacket(self, message):
        """
        Sends packets on the bus with 3.5char delay between frames
        :param message: Message to be sent over the bus
        :return:
        """
        start = time.time()
        timeout = start + self.client.timeout
        while self.client.state != ModbusTransactionState.IDLE:
            if self.client.state == ModbusTransactionState.TRANSACTION_COMPLETE:
                ts = round(time.time(), 6)
                _logger.debug("Changing state to IDLE - Last Frame End - {}, "
                              "Current Time stamp - {}".format(
                    self.client.last_frame_end, ts)
                )

                if self.client.last_frame_end:
                    idle_time = self.client.idle_time()
                    if round(ts - idle_time, 6) <= self.client.silent_interval:
                        _logger.debug("Waiting for 3.5 char before next "
                                      "send - {} ms".format(
                            self.client.silent_interval * 1000)
                        )
                        time.sleep(self.client.silent_interval)
                else:
                    # Recovering from last error ??
                    time.sleep(self.client.silent_interval)
                self.client.state = ModbusTransactionState.IDLE
            else:
                if time.time() > timeout:
                    _logger.debug("Spent more time than the read time out, "
                                  "resetting the transaction to IDLE")
                    self.client.state = ModbusTransactionState.IDLE
                else:
                    _logger.debug("Sleeping")
                    time.sleep(self.client.silent_interval)
        size = self.client.send(message)
        self.client.last_frame_end = round(time.time(), 6)
        return size

    def recvPacket(self, size):
        """
        Receives packet from the bus with specified len
        :param size: Number of bytes to read
        :return:
        """
        result = self.client.recv(size)
        self.client.last_frame_end = round(time.time(), 6)
        return result

    def _process(self, callback, error=False):
        """
        Process incoming packets irrespective error condition
        """
        data = self.getRawFrame() if error else self.getFrame()
        result = self.decoder.decode(data)
        if result is None:
            raise ModbusIOException("Unable to decode request")
        elif error and result.function_code < 0x80:
            raise InvalidMessageReceivedException(result)
        else:
            self.populateResult(result)
            self.advanceFrame()
            callback(result)  # defer or push to a thread?

    def getRawFrame(self):
        """
        Returns the complete buffer
        """
        _logger.debug("Getting Raw Frame - "
                      "{}".format(hexlify_packets(self._buffer)))
        return self._buffer

# __END__
